Various coordinate locating devices for locating the coordinates of an object are known. Some can detect the coordinates of an object from a pointing instrument, such as a pen, a fingertip, or a dedicated device. A user can input information with the pointing instrument accordingly.
Common techniques employed in conventional coordinate locating devices for locating the coordinates of an object include mechanical buttons, crossed light beams, acoustic surface waves, capacitance sensing, and resistive materials. Among these techniques, those employing crossed light beams are not limited by the display panel size and are therefore cost competitive.
For example, Yasuji Ogawa, U.S. Pat. No. 7,414,617 discloses a coordinate locating device for generating coordinates. The device comprises a pair of cameras positioned in an upper left position and an upper right position of a display.
Another example, Susumu Fujioka, U.S. Pat. No. 7,342,574, discloses a method for inputting information including coordinate data, comprising providing at least two cameras at respective corners of a display.
In another example, John L. Junkins, etc., U.S. Pat. No. 5,525,764 discloses a graphic input system comprising at least two primary scanning lasers for digitizing the coordinates of an object.
However, these conventional coordinate locating devices are all implemented with at least two light sources and two detectors (or two cameras). Moreover, since each light source and corresponding detector is disposed at the same position such as a corner of a display panel, only one shadow of the object can be formed by each set of light source and detector. The conventional coordinate locating devices are thus undesirably limited to determining the coordinate or gesture of a single object only and have limited applications.